In contrast to the Swiss load model used for new bridge structures (SIA 261), which has roots in a Europe-wide weigh-in-motion (WIM) study and considers the full design life of new structures, the model for existing structures (SIA 269) from 2005 is derived from load effects produced by traffic measured by country-specific WIM observations and considers a reduced return period.

With growing concerns regarding the scarcity of resources, efforts should be made to ensure safety by increasing the knowledge of loads and load-carrying mechanisms, rather than through overdesign. This paper presents the methodology employed to use WIM data for generating maximum expected load effects on bridges and thus give engineers a tool with which bridge load effects can be accurately derived from real traffic. A re-evaluation using the methodology outlined here began this year. It is planned to use the results of this for the next revision of the Swiss National Annexes to the Eurocodes and SIA 269.